Scientists with the Burned Area Emergency Response Team have finished their work to determine the impacts of the 27,000-acre Pocket Fire on the Mogollon Rim and in canyons along Oak Creek and north of Sedona.
They say the fire increased the risk of flash flooding but mostly burned at a low intensity.
KNAU’s Adrian Skabelund spoke with U.S. Forest Service hydrologist Kelly Mott Lacroix.
ADRIAN SKABELUND: We've seen a pretty active monsoon pattern just the last, like, couple of weeks. I'm just curious whether that challenges you guys at all in doing your work as a BAER team to kind of do what you guys need to do?
KELLY MOTT LACROIX: Yeah, great question. So the active monsoon that we have, that makes it so we have a shorter period of the day to do our work. But it also makes it easier to do our assessment because one of the big things we do is look at post-fire runoff.
And when you're getting actual runoff that you can look at, [and you can see] how much fell and how much is coming out, you can create more accurate models and predictions.
SKABELUND: So you don't need to look at a map and guess what's going to happen. You can just see what's potentially already happening right in front of you?
MOTT LACROIX: Yes, we can get a good sense for what the impacts of the fire might be and use those little bits of data to improve our modeling and then the areas that we think might be at risk.
SKABELUND: Based on your guys' field visits, can you describe what the area looks like post-fire, and I'm sure that varies from part to part.
MOTT LACROIX: It absolutely varies from part to part, and that variation has to do with what the soil burn severity looks like. An important thing to note is that there's two different types of burn severity: there's soil [burn severity] and there's vegetation [burn severity].
So you can see an area where the trees are all gone, it looks very black and charred, but actually [the fire has] moved through quickly enough so that those soils are still intact. And that's one of the most common things that people don't understand about these assessments.
And the soils still being intact is super important for recovery, as well as for how the area responds post-fire.
One of the things we're seeing is what we call a mosaic burn. So you have some areas that have a lot of higher vegetation and soil burn severity, and you have areas where it's low, which is good because that helps the watershed recover more quickly post-fire.
SKABELUND: Yeah, so you guys put out a report on specifically the soil burn severity, and the finding was about 65% low soil burn severity, and about 30% moderate or high burn severity. Break that down, what does that mean in layman's terms?
MOTT LACROIX: So that means that overall the effects of the fire will be relatively short-term in terms of the vegetation recovery. Doesn't mean we're going to have a big ponderosa pine forest back again where we had it before, but you'll start to see the grasses and the shrubs come back in [those areas of] low soil burn severity.
The risk from post-fire floods really depends on what sort of rain we get.
Many folks will remember the [2014] Slide Fire, and we didn't get a whole lot of post-fire impacts from flooding post-Slide Fire, but that's because we did not get the storms.
So this fire, with storms that we are getting, with storms that we will continue to get, we will see elevated post-fire floods within the West Fork of Oak Creek, and that drains into Oak Creek Canyon, for the remainder of the monsoon season at least.
SKABELUND: And just with these rains, just in the last weekend, we've seen Oak Creek running black with ash. Is that pretty typical?
MOTT LACROIX: Yes, it's absolutely typical. That's what we see after every single fire.
And the important thing to remember too, because we have monsoon systems, those are about five square miles. The fire is bigger than that, so you can have some of the ash flushed out on parts of the fire flow out [and downstream], and then you can have another storm that hits another part of the fire and see more ash flowing out.
So we should expect to see ash flows through Oak Creek Canyon for probably the rest of monsoon.
SKABELUND: Were you guys able to get into West Fork at all or some of those canyon areas? I know, certainly during the main firefighting operations, folks really weren't able to get in there at all. I'm just curious about what those areas looked like.
MOTT LACROIX: One of the things I noted in West Fork is, down in the channels, you still have a lot of the vegetation left, which is good. That will help with recovery.
[It’s] obviously spotty, some places where the vegetation has been burned.
Most of the higher burn [severity] is actually up above in the canyon area on West Fork.
SKABELUND: Kelly, thanks so much for giving us some of your time today.
MOTT LACROIX: My pleasure.
